Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $61.34   10.174%   $67.5807   $67.58   $67.60   $67.60  
  Purchase #2 $100.35   11.332%   $111.7217   $111.72   $111.70   $111.70  
  Purchase #3 $246.95   11.830%   $276.1642   $276.16   $276.15   $276.20  
  Purchase #4 $12.94   3.453%   $13.3868   $13.39   $13.40   $13.40  
  Purchase #5 $163.30   8.599%   $177.3422   $177.34   $177.35   $177.30  
  Purchase #6 $8.74   9.333%   $9.5557   $9.56   $9.55   $9.60  
  Purchase #7 $19.57   4.315%   $20.4144   $20.41   $20.40   $20.40  
  7 purchase totals = $613.19       $676.1657   $676.16   $676.15   $676.20